I see you're new to powergaming, then.
Try either Assassin/cleric (DuHM + RM + Staff of the Ram + assassination, anyone?) or Assassin/mage (mislead exploit), maybe even Assassin/fighter (using assassination) if you're after damage. Fighter/mages suck in that regard.
Note: this is in the context of BG2/ToB.
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Nope. Been a powergamer since Diablo came out.